This invention relates to a half shaft assembly and in particular a half shaft assembly utilized to rotatively drive a vehicle wheel.
Automotive vehicles have a rigid frame commonly referred to as a chassis. The chassis is typically supported on four or more wheels by a suspension system. The suspension system includes a spring and a damper commonly referred to as a shock absorber or strut. The suspension system allows for relative movement between the wheel of the vehicle and the chassis while still supporting the vehicle. Relative movement between the chassis and wheel is required to allow the wheel to react to a contour of a road surface. In the case of drive wheels, the suspension system must provide for relative movement between the wheel of the vehicle and the chassis while still driving the vehicle. Additionally, on the front end of the vehicle, the suspension system accommodates a steering system to direct the vehicle by turning the vehicle front wheels.
An engine which powers the vehicle is rigidly connected to the chassis. An output shaft of the engine transfers torque to a transmission. The transmission is also rigidly connected to the chassis. In a front wheel drive vehicle the engine and transmission are typically mounted to the chassis transverse to a vehicle's major axis, and a transaxle associated with the transmission transfers torque to the front wheels. For purposes of discussion, as used herein the term "transmission" is inclusive of a transaxle.
A separate half shaft assembly, sometime referred to as a stub shaft, is commonly used to transfer torque from the transmission to each front wheel. The half shaft assembly includes a half shaft mounted transverse to the major longitudinal axis of the vehicle. The half shaft has an inboard end mechanically coupled to a transmission output shaft. The half shaft has an outboard end mechanically coupled to a wheel axle.
A universal joint is a mechanical coupling device which provides a rotational driving connection between two rotatable shafts, while permitting such shafts to be oriented at an angle relative to one another. In the example of a front wheel drive vehicle, an outboard universal joint is used to provide a rotational driving connection between the half shaft and the front wheel axle of the vehicle. An inboard universal joint provides a mechanical coupling between the half shaft and the output shaft of the transmission. The universal joints allow the transmission to be fixed to the chassis while the wheel has relative movement with respect to the chassis.
Universal joints are commonly classified by their operating characteristics. One important operating characteristic relates to the relative angular velocities of the two shafts connected thereby. In a constant velocity type of universal joint, the instantaneous angular velocities of the two shafts are always equal, regardless of the angle of rotation. In a non-constant velocity or Cardan type of universal joint, the instantaneous angular velocities of the two shafts vary with the angle of rotation, although the average angular velocities for a complete rotation of each driveshaft are equal.
A typical structure for a constant velocity universal joint includes a cylindrical inner race connected to a first rotative shaft and a hollow cylindrical outer race connected to a coupled second rotative shaft. The outer surface of the inner race and the inner surface of the outer race have respective pluralities of grooves formed therein. The grooves extend linearly, i.e., generally in the direction of the driveshafts, and have generally semi-circular cross sectional shapes. Each groove formed in the outer surface of the inner race is associated with a corresponding groove formed in the inner surface of the outer race. A torque transmitting ball is disposed in each of the associated pairs of grooves. The balls provide a driving connection between the inner and outer races. An annular cage is typically provided between the inner and outer races for retaining the balls in the grooves. The cage is provided with a plurality of circumferentially spaced openings for the above noted purpose.
In a typical half shaft assembly for a front wheel drive vehicle, constant velocity universal inner joint races are connected to outboard and inboard ends of the half shaft. Outer constant velocity universal joint races are connected to the front wheel axle and to an output shaft of the transmission. Constant velocity universal joints are lubricated with a grease lubricant. Constant velocity universal joints should be protected from dirt, moisture and other environmental contaminates which could damage the universal joint. A first flexible convoluted boot is provided to protectively enclose the inner and outer races of the inboard constant velocity joint. A second flexible convoluted boot is provided to protectively enclose the inner and outer races of the outboard constant velocity joint. Each of the boots requires two clamps. One clamp secures a first convergent end of the boot to the half shaft. A second clamp secures a second divergent end of the boot to the outer race of the universal joint. It would be desirable to replace the two required protective boots with a single boot to simplify the half shaft assembly. It would be desirable to lower the amount of clamps required, thereby lowering the material cost and assembly time required for the half shaft assembly.